<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>缓存全局变量</title>
</head>
<body>
  <input type="button" value="btn" id="btn1" />
  <input type="button" value="btn" id="btn2" />
  <input type="button" value="btn" id="btn3" />
  <input type="button" value="btn" id="btn4" />
  <p>111</p>
  <input type="button" value="btn" id="btn5" />
  <input type="button" value="btn" id="btn6" />
  <p>222</p>
  <input type="button" value="btn" id="btn7" />
  <input type="button" value="btn" id="btn8" />
  <p>333</p>
  <input type="button" value="btn" id="btn9" />
  <input type="button" value="btn" id="btn10" />

  <script>
    function getBtn() {
      let oBtn1 = document.getElementById('btn1');
      let oBtn3 = document.getElementById('btn3');
      let oBtn5 = document.getElementById('btn5');
      let oBtn7 = document.getElementById('btn7');
      let oBtn9 = document.getElementById('btn9');
    }

    function getBtn() {
      let obj = document;
      let oBtn2 = obj.getElementById('btn2');
      let oBtn4 = obj.getElementById('btn4');
      let oBtn6 = obj.getElementById('btn6');
      let oBtn8 = obj.getElementById('btn8');
      let oBtn10 = obj.getElementById('btn10');
    }
  </script>
</body>
</html>